PART 1 Special risks groups - Pregnancy Flashcards
During pregnancy, most drugs can ____ and _____.
Cross the placenta and expose the baby to their effects.
Factors affecting placental drug transfer and drug effects on the fetus
- Drug physiochemical properties.
- Duration of drug exposure.
- Distribution in different fetal tissues.
- Stage of placental and fetal development.
- Effects of drugs used in combination.
- Rate at which drug crosses placenta and amount reaching fetus.
Pharmacokinetic changes in GASTROINTESTINAL ABSORPTION
- Decreased GI motility and reduction in gastric acid secretion.
- Increase in gastric pH, therefore negatively affects drugs that require acidic pH for absorption.
- Nausea and vomiting
Pharmacokinetic changes in LUNG ABSORPTION
- Cardiac and tidal volumes increase by approx. 50% in pregnancy.
- Hyperventilation and increased pulmonary blood flow.
Pharmacokinetic changes in TRANSDERMAL ABSORPTION
- Vasodilatation leads to increased tissue perfusion.
- Absorption on IM administration is highly effective.
Factors affecting DRUG ABSORPTION in Pregnancy.
Hint - LMP
- Lipid solubility
- Molecular size
- pH
Lipid solubility factor
- Lipid soluble drugs (e.g. Thiopental) easily diffuse across the placenta.
- Impermeability of the placenta to polar compounds is relative rather than absolute (whole thing).
- That’s if high enough maternal-fetal concentration gradients are achieved, polar compounds cross the placenta in measurable amounts (e.g. Salicylate).
Molecular size factor
- Influences the rate of transfer and amount of transfer.
- Drugs having molecular weight:
A. 250-500 cross easily.
B. 500-1000 cross with more difficulty.
C. >1000 cross very poorly.
Factors affecting DRUG DISTRIBUTION in pregnancy.
- Protein binding
- Body fat
- Total body water
Total body water factor
Total body water increases due to hemodilution, so large volume of distribution for water soluble drugs.
Total body water factor
Total body water increases due to hemodilution, so large volume of distribution for water soluble drugs.
Body fat factor
- Body fat is increased and acts as a reservoir for lipid soluble drugs.
- These lipid soluble drugs can increase and accumulate in body fat, causing toxicity.
Factors affecting DRUG METABOLISM in pregnancy
- Blood flow (cardiac output)
- Hepatic clearance
Blood flow factor
Hepatic metabolism is increased through blood flow to liver.
Hepatic clearance factor
- Hepatic clearance = ability of the liver to extract and metabolize a drug as it passes through the liver.
- Drugs metabolized by the liver have increased clearance.
Factors affecting DRUG ELIMINATION in pregnancy
- Renal blood flow
- Glomerular Filtration rate
Renal blood flow factor
Is increased or doubled; therefore there is rapid elimination of drugs excreted by the kidneys.
Glomerular Filtration rate factor
- Is increased….
3 things determine the magnitude and seriousness of a drug on fetal development
- Fetal age
- Drug dosage
- Potency
Drug use during lactation
- Most drugs are detectable in breast milk.
- Concentrations are usually low, preventing infants from receiving therapeutic amounts.
Recommendations for feeding mothers
- Take safe drug 30-60 mins after nursing and 3-4 hrs before next feeding.
- Avoid usage of toxic drugs or discontinue breast feeding.
TETRACYCLINE effects on infants during lactation
Risk of permanent tooth staining in infant.
ISONIAZID effects on infants during lactation
Risk of pyridoxine deficiency in the infant.
BARBITURATES effects on infants during lactation
Lethargy, sedation and poor suck reflexes.
IODINE effects on infants during lactation
Thyroid suppression and risk of cancer.
DIAZEPAM effects on infants during lactation
Drug accumulation and sedation.
CHLORAL HYDRATE effects on infants during lactation
Drowsiness if infant is fed at peak.
Therapeutic effect of drugs on fetus
- EXAMPLES
Drugs are administered to pregnant women targeting fetus.
- Corticosteroids = used for lung maturation.
- Phenobarbitone = prevents neonatal jaundice.
- Zidovudine or Nevirapine = inhibits transmission of AIDS to fetus from mother.
Predictable toxic effect of drugs on fetus
- EXAMPLES
- Opioids = respiratory depression.
- ACE inhibitors = congenital anomalies.
- Diethylstilbestrol = vaginal carcinoma in female offspring after puberty.
Describe a Teratogen
- Any drug or substance that produces characteristic sites of malformation with selectivity for certain organs.
- Also exerts its effect at a particular stage of fetal development.
(An agent or factor which causes malformation of an embryo)
Examples of malformations a teratogen causes
Clubfoot, neural tubal defects, missing or malformed limbs etc.
What happens when there is continuous exposure to a teratogen?
May produce cumulative effect or may affect multiple organs which are undergoing development.
E.g. Facial abnormalities
Drugs that treat CONSTIPATION
common problems in pregnancy & safe drugs
Mild purgative like Senna
Drugs that treat URINARY TRACT INFECTIONS (UTIs)
common problems in pregnancy & safe drugs
- Ampicillin
- Amoxycillin
- Cefuroxime axetil
Drugs that treat PEPTIC ULCER
common problems in pregnancy & safe drugs
- Sucralfate
- H2 blockers
Drugs that treat NAUSEA & VOMITING
common problems in pregnancy & safe drugs
- Pyridoxine
- Meclizine diphenhydramine
Drugs that treat MALARIA
common problems in pregnancy & safe drugs
- Chloroquine
- Quinine
- Proguanil
Drugs that treat HIV INFECTION
common problems in pregnancy & safe drugs
- Zidovudine
- Nevirapine
Drugs that treat EPILEPSY
common problems in pregnancy & safe drugs
Must be used in lower dose:
- Sodium valproate
- Carbamazepine
